Decorative aluminum surface



June 21, 1960 N. MOSTOVYCH ETAL DECORATIVE ALUMINUM SURFACE Filed May28. 1957 INVENTORS Mam/1s MOSTOVICH n/v BY WALTER nm/mm, J/a

DECORATIVE ALUMINUM SURFACE Nicholas Mostovych, Louisville, and WalterA. Mitchell,

Jr., Anchorage, Ky., assignors to Reynolds Metals Company, Richmond,Va., a corporation of Delaware Filed May 28, 1957, Ser. No. 662,141

12 Claims. (Cl. 204-29) This invention relates to ornamental aluminumand aluminum alloy products and to a method for producing the same.

An object of our invention is the production of aluminum and aluminumalloy products having highly valuable decorative and ornamentalcharacteristics, and in which products the decorative finish achievednot only affords protection against corrosion of the underlying metalbut itself is durable under many and varied conditions of exposure.

Another object is the provision of products of the character indicatedin which the ornamental surface finish introduces to the eye a varietyof different shades or tones of any particular color of the finish.

A further object of our invention is the provision of finish is in anintegral filmformed of the metal itself.

Another object is that of providing a direct and thoroughly practicalmethod for producing aluminum and aluminum alloy metal products, havingornamental and decorative properties.

A still further object of our invention is the provision of a method forcoloring aluminum and aluminum alloys which with regard to a particulardecorative color application simultaneously produces varied shades andtones of the color from a given uniform source of the color.

Other objects of the invention in part will be obvious and in part willbe pointed out more fully hereinafter.

The invention accordingly consists in the features of construction,combination of elements and arrangement of parts, and in the severalsteps and the relation of each of the same to one or more of the othersas described herein and the scope of the application of which isindicated in the following claims.

In the drawing which forms a part of this specification,

Figure 1 represents an enlarged corner section of lightly etched metaltreated in accordance with the principles of the present invention.

Figure 2 is similar to Figure 1 except the etching action has continueduntil a pronounced surface relief results.

Figure 3 is a representative cross-section of Figure 2.

Figure 4 shows a metal sheet whose large crystals have become elongatedduring roll bonding to a base sheet.

Figure 5 represents a ribbed sheet whose ribs have been considerablyreduced in thickness by cold working.

Figure 6 represents a ribbed sheet whose ribs have been moderatelyreduced in thickness by cold work.

Figure 7 represents a ribbed sheet whose ribs are only slightly reducedin thickness by cold work.

As conducive to a clearer understanding of certain features of ourinvention it may be noted at this point that aluminum, by which we meanto call the high purity metal itself or aluminum-base alloys, arerelatively lightweight metals Which fulfill a wide variety of well knownneeds and for example in so doing take the form of sheet, strip, bars,rods, tubes, structural members, household articles and utensils,hardware, trim, blocks and a host of other shapes, articles andproducts. There is a great possible outlet for ornamental and decorativeproducts of the metal in the form of any of the products just named andthere are many other possible outlets, illustratively United StatesPatent 0 products of the character indicated in which the decorative iceornamental Wall panels for inside or outside use in buildings, store orrestaurant furnishings, objects of art, ornamental edgings, frames andespecially extruded, rolled, or spun articles of manufacture but inorder to supply this demand a solution enabling the commerciallyfeasible production of widely useful ornamental and decorative finisheswhich are pleasant, beautiful and durable become necessary.

An outstanding object of our invention accordingly is the commerciallypractical production of decorative and ornamental aluminum and aluminumalloy manufactures having durable surface beauty and which production ingeneral lends itself to the provision of any of a great variety ofproducts having the desired surface finish.

Referring now more particularly to the manner of producing a decorativeor ornamental product, we find that aluminum, by which we mean the highpurity aluminum metal itself or any of a variety of aluminum-base alloysincluding heat treatable alloys responds to anodizing treatment and dyecoloring with most striking after .effect if at least the metal grainsin certain areas of the metal surface first are adjusted to coarse sizeswhich are visible to the naked eye and the metal is etched beforetreatment in the anodizing bath. When the faces of the macroscopiccrystals undergo the anodizing treatment, these faces take on byalteration a thin oxide film in the bath and thus the underlying metalis shielded and has its resistance to corrosion appreciably enhanced,but of further importance the oxide when introduced to dye, verydistinctively takes on different tones and hues of the dye color overthe macroscopic crystal faces depending upon which of the anodized grainfaces in the great maze of crystals the dye encounters. To the eye of anobserver, the depths of the color tones actually seem to alter when theviewing angle is changed. A most beautiful, varied and interestinganodized aluminum surface thus becomes a reality. The dye coloring iscarried in the electrochemically derived oxide film which itself isintegral with the underlying metal.

Very. pleasing ornamental effects on aluminum thus are had from ouranodizing and dyeing treatments where the metal subjected to thoseoperations has crystals developed :by heat, treatment to predominatelymacroscopic sizes at least in localized surface areas or over the entireproduct surface. The majority of the macroscopic crystals preferablyhave sizes anywhere in the approximate range of a fraction of amillimeter to three centimeters or more when measured in plan across thecrystal boundaries on the metal surface. For bringing the crystals tosizes falling within this approximate range we usually impose strain inthe metal such as by cold rolling, bending, pressing, drawing, orstretching from a substantially dead-annealed or stress-free conditionof the aluminum body to which the strain is to be applied, and thenfollow with recrystallization heat treatment. Grain size is primarily afunction of strain, annealing temperature and heat-up rate. With littleor no strain, no crystal growth is induced. With a critical amount ofstrain, a large grain size results. As the strain is increased above thecritical amount, the grain size diminishes in size, rapidly at first andthen more slowly. Small strain and high annealing temperatures producethe largest crystals. A strain which is equivalent to about 1% to 15%reduction in thickness of the metal followed by annealing atapproximately' 600 F. to 1150 F. for re-crystallization are preferred.The period of time which the metal is held at the rte-crystallizationtemperature to grow crystals of desired size may vary considerablydepending upon such factors as whether the aluminum is in the form ofhigh purity aluminum or is some specific aluminum base alloy, theparticular amount of strain imparted, the actual temperature ofre-crystallizationheat treatment, and heat-up 3 rate. For strains andtemperatures within the preferred ranges of strain andre-crystallization temperatures hereinbefore noted, a period of aboutten minutes to three hours time is usually satisfactory for developing acontinuous crystal lattice in the metal which has been so strained.

The coarse grained aluminum product is subjected to an etching orcrystal revealing treatment and for this purpose We use one or moreacids such as hydrochloric acid in combination with nitric acid,sometimes with additions of hydrofluoric acid, in an aqueous bath. Acaustic solution may also be used. The metal conveniently is immersed inthe crystal revealing bath for a period of time which produces a clean,etched aluminum surface having the crystal faces exposed so that thefaces and their boundaries are clearly visible to the naked eye. For amild etch and to give only a slightly high-low crystal pattern on themetal surface we restrict the etching period to just a few minutes timeand then remove the metal, at which point some of the crystal faces onthe surface are slightly outward from others of the crystal faces makingup the surface. In this condition of slight relief, (see Figure 1), themetal may be finished by anodizing and dying to produce the coloredproduct. In other instances the etching treatment is prolonged to givepronounced depth dimensions (see Figure 2) which are derived by theselective action of the etching solution on the various crystal faces.Some of the faces are selectively eaten away and finally the relief ofsome of the macroscopic crystal faces with respect to others is sopronounced as to introduce substantial physical depths.

A durable and highly effective etching bath which we prefer for thepurpose is one heated to approximately 120 F. and which contains inapproximate amounts, by volume, to 40% nitric acid, 20% to 40%hydrochloric acid, and the remainder substantially all water. To thismay be added 1% to 3% hydrofluoric acid if etching at room temperatureis desired. The acids identified above usually are commercial grades ofthe acids. By treating the coarse grained aluminum in the bath for aboutone minute to ten minutes time a mild etch results and by prolonging thetreatment for a time ranging up to an hour or more a relatively severe.action takes place to produce a surface having certain grain faces agreat deal deeper than the faces of adjacent grains. After the etchingaction has progressed the desired amount, the metal is removed from thebath and .is rinsed clean in water.

After etching the ahuninum and exposing the crystal faces and theirboundaries, We make the metal the anode of an anodizing bath andaccordingly electrolytically oxidize the exposed areas of the productsuch as the faces of the various macroscopic crystals. Usually weanodize the entire metal surface and thus add the protection of theoxide layer. We prefer to use an electrolytic bath which producesrelatively transparent oxide film on the metal surface for, with a filmof that sort, especially desirable optical properties are gained for thefinal product. In Figure 3 can be seen the difference in surfaceroughness between the more resistant and only slightly etched crystalsand those crystals which are less resistant which have been deeplyetched. The rough surface of the'less resistant crystals has a greaterthickness of oxide film thereon which will absorb more dye than the moreresistant crystals. Also, the surface roughness of the less resistantcrystals causes a diflusion of the light in contrast to the highreflectivity of the mirror-like surface of the more resistant crystalfaces. Thus, after anodizing the coarse grained metal, some of thecrystal faces have relatively high specular reflectivity and other faceshave a more difiuse reflectance, and this is all the more prevalent whenthe anodized fil'm is itself transparent. On anodizing, it appears thatthe resulting oxide film thickness depends upon orientation of eachparticular crystal and, in fact, thickness may vary as much as or 4 morewith crystallographic direction. Those crystal faces which have beenmost etched during the etching and crystal revealing treatment will havethe heaviest oxide film and most diifuse surface after anodizing andaccordingly absorb more dyestufl than a face which has been relativelyresistant to etching. On being colored, certain crystals-on the metalsurface are revealed in lighter color than are others with the resultthat many and different color shades and hues attract the eye, and bymaking the oxide film transparent, as preferred, 'the reflectance of thealuminum under the oxide film contributes a metallic aspect through thecolor. A sulfuricacid anodizing bath is preferred for it gives a verygood transparent oxide film on the aluminum and the film has excellentdyeing properties. A typical sulfuric acid anodizing bath which weemploy for the purpose is given as follows along with certain operatingconditions which have been found to be practical with use:

15% sulphuric acid (by weight) 70 F. electrolyte temperature 12 amperessquare foot current density (direct current) '15 to'3O minutes anodizingtime In coloring the oxide film we usually immerse the aluminum .productin a dye bath having the desired color. Among the types of dyes utilizedare well known commercial dyes such as ferric ammonium oxalate for goldand Alizarin 'Saphiral B for blue. The colors applied to the oxide may,of course, be any of a wide variety including red, pink, :yellow,orange, green, blue, black, 'bufi, brown, 'or gold, depending on the dyeselected. After coloring, the film is sealed to advantage such as bytreatment in boiling water, steam, or other sealing media.

Sometimes, especially when high purity aluminum is used, the surface istoo bright for the intended purposes. This brightness may be reduced bya low temperature, high current density anodizing treatment, preferablyusing A.C. current although DC. current is also satisfactory. AC.anodizing for a few minutes at 40 to 60 F. and a current density of to300 amperes per square foot gives very satisfactory results. Another wayof reducing brightness is by dislocating and straining the crystalsafter the recrystallization treatment but before the crystal revealingetch.

Our process also readily lends itself to the frequently useful aspect ofmasking out with a suitable masking composition any desired areas of theoxide film which are not to be colored in the dye bath, thus tocontribute to ornamentation. .Also, the high spots may be dyed one colorand the low spots a different color by means of well known masking andbleaching techniques. After dyecoloring the exposed areas of the film,the masking composition is -removed and the entire film then is sealed.This selective masking may also be employed to present the action of thegrain revealing etch in selected areas if such be desired.

In making wrought aluminum products such as sheet or strip, startingfrom ingot the metal conveniently is reduced by a series of hot and coldrolling passes to a gauge which is somewhat thicker than the desiredfinal product. The cold reductions are accompanied by annealing stepswhich destroy the effects of cold working. The reductions and annealingtemperatures introduced at this point usually are conducive to theformation of grains of microscopic sizes and as a further result themetal is soft, stress relieved, and ready for further cold work. Thenafter the last of these cold reduction passes and annealing treatments,as described, the metal is ready to receive a critical amount of coldwork which is needed for growing crystals of macroscopic sizes. Thus, bycold-deforming the dead-annealed aluminum sheet or strip, such as byforming, bending, stretching or rolling .to introduce amounts of strainwhich are commensurate with strains developed by a cold reduction inthickness ranging from 1% to 15%, or somewhat more, we prepare the metalfor crystal growth. Then, on heating the metal up to 600 F. to 1150" 'F.in an annealing furnace, crystals of macroscopic sizes grow while theheating is continued. To a degree, the heat-up rate controls theultimate sizes of the grains for the same amount of strain. A highheat-up rate gives smaller crystals than where the rate is lower and inthis connection relatively slow rates up to 1000 F. per hour arepreferred for attaining annealing temperature. Heating the metal forabout ten minutes to thirty minutes, especially at the lower end of thepreferred range of re-crystallization temperatures given, usuallyproduces uniform aquiaxed crystals which in size are approximately equalto the thickness of the metal sheet or strip. A longer annealing time,especially at a higher temperature in the preferred heating rangeusually favors continuous crystal growth and continuous migration of thecrystal boundaries resulting in larger grains as viewed in the plane ofthe surface of the sheet or strip. By prolonging the annealing periodand using annealing temperatures which are close to the melting point ofthe metal, very large crystals as viewed in the plane of the sheet orstrip develop which are some one or more centimeters in size acrosstheir opposite boundaries. This type of crystal pattern comes mostreadily from aluminum alloys having a crystal inhibiting phase such asinsoluble impurities.

Since the aluminum has been re-crystallized, it is in the soft fullyannealed condition. In order to impart to the aluminum hardness andstrength, which is sometimes desirable, it is necessary to cold work thealuminum after recrystallization or else use a heat treatable alloywhich is given a solution heat treatment to improve same after therecrystallization treatment. The heat treatable alloys and the solutionheat treatment necessary for making them strong are well known to thoseskilled in the art. Both in the specification and claims,re-crystallized aluminum which is either cold worked or made from a heattreatable aluminum alloy which has been solution heat treated isreferred to as strong aluminum. Further, it is to be understood thatsolution heat treated aluminum means a heat treatable aluminum alloywhich has been solution heat treated to improve its physical properties.

Our process lends itself to such modifications as rolling or otherwiseattenuating the coarse grains in the aluminum product and this, forexample, is done immediately after growing the crystals by therecrystallization heat treatment already described. The coarse grainsare soft and elongate in the direction of working such as to give astriated crystal pattern on the metal surface, illustratively a surfacehaving the crystal pattern represented in Figure 4 of the drawing. Afterelongating the crystals by working, .the metal is etched to expose thecrystal faces, is anodized and colored in the manner hereinbefore setforth. Rolling to attenuate the coarse grains often is practiced by usin order to increase the properties of the metal by the cold workingwhile simultaneously achieving the attractive elongated grains. Coldworking of the metal after recrystallization to make strong aluminum canbe accomplished in numerous ways. For example, the aluminum may beflexed back and forth by passing through a series of rollers arrangedsimilar to those used to straighten wire. Also, the rolling may be usedfor the further purpose of roll cladding a sheet or strip of the coarsegrained aluminum to a stronger backing (see also Figure 4) which forexample may be a sheet of other metal such as an alloy of aluminumhardened by heat treatment. Such rolling and bending has to be donebelow the recrystallization temperature in order to preserve the largegrains. Quite often the aluminum which we treat in accordance with ourprocess is the highly pure metal itself since it is particularly easy tocontrol from the standpoint of growing grains of desired size and isquite amenable to the growth of grains of uniform size and to securehigh brightness after anodizing, yet

e the metal is deficient in physical strength for certain needs. By rollcladding this metal onto a strong backing, strength or otherrequirements are conveniently met and a highly ornamental product isreadily had by finishing in accordance with our process.

When critically straining the metal preparatory to growing grains ofmacroscopic size we often vary the amount of strain from area to area ofthe metal and thereafter by heat treatment grow crystals in one or moreof the areas which are larger than the crystals in areas elsewhereorfthe surface. The crystals illustratively may be of macroscopic sizesin all of the areas or of macroscopic size in certain of the areasdepending upon the stress pattern imposed and the subsequent heating.'Ihus, sometimes strain is developed to a sufiiciently high degree insome of the areas to preclude large grain growth entirely and thus thegrains remain invisible to the naked eye after heat treatment whichgrows macroscopic size grains in other areas which were less strained.Selective straining of the metal may be achieved in many possible ways.As a first example we have pressed a design into an annealed aluminumsheet or strip. Thus, subsequent heat treatment for growing crystalswill give large crystals in the area of the design.

Certain ribbed sheet aluminum products which we frequently provide aremade to have raised ridges which define valleys between the ridges,these ridges for example being spaced parallel ribs running the lengthof the metal body. Then starting with the ribbed product in adead-annealed condition we imposed varying strainon the ridges andvalleys or exclusively strain either the ridges or the valleys as byrolling, peening, pressing, or the like. The strain differential betweenridges and valleys on' re-crystallization heat treatment accordingly ismade great enough to induce marked differences in the sizes of grains onthe high and low areas whether the grains in several areas becomemacroscopic with heat treatment or whether the grains are macroscopicexclusively on the ridges or the valleys. In other instances we roll theridges completely into the plane of the valleys and in so doing impose arelatively light strain on the valleys and high on the ribs, and thengrow grains which produce a pattern commensurate with the stress.Examples of the above are illustrated in Figures 5, 6 and 7. In Figure 5the ribs were reduced 22% to give microscopic grains on the ribs andmacroscopic grains in the slightly worked valleys. The ribs of Figure 6were reduced 8% to give small grains on the ribs and larger grains inthe valleys. The ribs of Figure 7 were only reduced 1% to give largegrains on the ribs with no visible grains in the-unworked valleys.

We frequently resort to localized flexing of deadennealed aluminumsheet, strip, or the like to vary the strain pattern before crystalgrowth heat treatment. Stamping or pressing an emblem or the likeagainst the metal surface to introduce localized strains in accordancewith particular areas of the emblem is a further alternative, thus toproduce a strain impression which in accordance with macroscopiccrystals develop in at least enough of the areas to delineate the emblemor other pattern on heat treatment. The emblem or pattern strainimpression .of course lends itself to being repeated at intervals 'onthe metal surface, either alone or with other emblems on patterns topluralize the ornamental effect.

In those instances Where certain areas on the product surface arecharacterized by a microscopic grain structure while other areas on thesame surface have developed grains of macroscopic size after heattreatment, etchcing of course brings out the coarse grains, but fails toreveal the microscopic grains to the naked eye. The entire productsurface advantageously is anodized to gain the benefit of the protectiveoxide film even over those areas which have the minute grains, and onapplying dye color to the film surface the coarse grained areas take ona variated color shade aspect, as previously exgold and diffuse yellow.

, 7 plainedfwhile those portions of the'film overlying the areas havingthe minute grains retain a more even tone.

EXAMPLE A 0.020 inch gauge sheet of high purity aluminum is providedcontaining approximately 99.87% aluminum and the remainder small andincidental amounts of impurities of which iron and silicon are presenteach in amounts up to 0.06% maximum. The sheet is annealed at about 700F. for approximately one hour in a suitable annealing furnace and thenis air cooled to room temperature giving full stress-relief andmicroscopic size of the metal grains. Then, the dead annealed all);minum sheet is rolled so as to elongate it about 8%, and accordinglyintroduce a substantially constant amount of strain throughout thesheet. Thereafter, the sheet is annealed at about 1100 F. for two hoursusing a slow heat-up rate of less than about 1000 F. per hour to attainannealing temperature. After air cooling the heated treated product toroom temperature, it is etched for about three minutes at 120 F. in anacid bathcontaining by volume, 35% commercial nitric acid, 40%commercial hydrochloric acid, and the remainder sub? stantially allwater. The mildly etched product is rinsed in clean water and then theentire sheet is anodized in an aqueous acid bath containing by weight15% sulphuric acid and the remainder substantially all water. Thebath ismaintained at about 70 F. during this treatment and the anodizing periodendures for approximately fifteen minutes using direct current and acurrent density of 12 amperes per square foot of the aluminum metalsurface being anodized. Thus, a transparent oxide film forms on theexposed grain faces of the metal. The anodized product is rinsed free ofelectrolyte in clean water and thereafter is immersed in a dye bath offerric ammonium oxalate which imparts a gold color to the oxide film.The colored film is sealed by immersion for about fifteen minutes inwater heated to 200 F. and the colored product is removed and dried. Thegrain faces on the surface of the sheet, though differently oriented anddifferent in outline at their boundaries, each measure about 0.10 inchin diameter. The entire aluminum sheet metal surface treated ischaracterized by the presence of bright gold with other shades of goldand diffuse yellow and has great beauty such as for ornamental wallpanel use or the sheet may serve any of a wide variety of other possibleuses. On occasions we cut the sheet into blocks such as those whichserve as substitutes for wall block tile, or make strips which forexample are used for trim, edgings, striping, or the like, or the sheetis otherwise cut or fabricated to desired ornamental shape.

A 0.020 inch gauge alloy aluminum panel containing about 0.20% to 0.40%manganese, 0.90% to 1.2% magnesium, copper 0.05% maximum, iron 0.15%maximum, silicon 0.1% maximum and the remainder substantially allaluminum treated in accordance with Example I except for being subjectedto a grain growing annealing heat of about 1000" F. for two hours, has abeautiful gold finish including bright gold with other shades of Thegrain faces on the surface of the panel each measure about 0.30 inch indiameter.

EXAMPLE III A homogenized cast aluminum alloy billet containing seventyto ninety seconds to an extrusion temperature s 0 F. t and. 3 0 While-s9h a e iving intermediate products. The extruded lengths are cooled instill air and subsequently are stretched cold at room temperature toachieve an elongation of about 8%. Following this, the products aresubjected .to a crystal growing heat treatment and solution heattreatment a 925 F. to 1025" F. for about two hours in. an annealingfurnace and thereafter are dip quenched in water to room temperature. Anaging heat treatment then is given the metal products, this being a heatat 350 F. for three hours to improve the ultimate strength of theproducts. From this point on, the extruded prodnets are etched,anodized, dyed and sealed consistent with the same steps and workingconditions set forth in Example I. The coloring achieved on the metal isin general somewhat less bright than on the products .in Examples 1 andII but nevertheless is very attractive in the subdued color sense. Thegrain size is quite uniform and on the order of 0.10 inch diameteracross each crystal face exposed.

EXAMPLE IV A ribbed material as shown in Figures 6, 7 and 8 of aluminumalloy 5,357 comprising approximately 0.3% manganese, 1.0% magnesium, amaximum of 0.1%

silicon, a maximum of 0.15% iron, a maximum of 0.05%

copper and the remainder aluminum was soft annealed at 750? F. forthirty minutes. They were then cold rolled to produce strain. The amountof reduction on the ribs varied from 1.-22%. After rolling, the metalwas annealed at 1080" F. for a period of two hours to re-crystallize.The metal was etched, anodized and dyed as in Example I. Results were asfollows:

When the ribs received about 1% reduction, crystals were formed on theribs with no noticeable crystals in the valleys. The ribs were brightand the valleys were etched in appearance.

When the ribs received about 8% reduction, small crystals appeared onthe ribs with large crystals in the valleys.

When the ribs received 22% reduction, the valleys were reduced a fewpercent, the ribs had no noticeable crystals and .was of an etchedappearance whereas bright large crystals appeared in the valleys. i

All three samples presented a very attractive appearance.

EXAMPLE V Ashtrays were produced by a two-step drawing with aluminumalloy 1187 comprising at least 99.87% a111 minum with the remainderbeing impurities with a maxiof 0.06% silicon, 0.06% iron and 0.005%titanium.

In thefirst step, the metal was formed up to After soft annealingbetween 700800 F., final forming was done upon the remaining amount upto. 15% to induce critical strain. After annealing at 1050" F. for onehour, the sample was etched, anodized dyed above, presenting a verydecorative finish. In order to get uniform crystals, proper dies shouldbe used to assure uniform critical strain during the final operation. H6' EXAMPLE v1 Dinner plates of regular household size and shape wereformed by shallow drawing with the alloy of Example .IV. Group A wasannealed for two hours at 1050 .F. Group B at 800 for three to fiveminutes. Group .C at 800 F. for seven to ten minutes. After annealing,the plates were etched, anodized and dyed as above. The followingresults were obtained:

Group A. ,These plates showed complete coverage of small and largecrystals depending on strain.

Group B.These plates showed one ring of smal crystals at the place ofgreatest strain. V Group C.T hese plates showed two rings of smallcrystals at the two places of greatest strain.

All plates had an appealing effect.

In practicing the process herein described, a sheet of aluminum can becritically strained and then annealed to provide the grain growthdesired. Subsequently, an ar-, ticle can be formed from this sheet suchas a lamp shade made by spinning. This formed article is then etched toreveal the grain structure which simultaneously removes the tool marks.After anodizing the articles and dying them, they take on a veryattractive appearance.

Thus it will be seen that in this invention there is provided a methodand products in which the various objects hereinbefore noted, togetherwith many thoroughly practical advantages, are successfully achieved. Itwill be seen that the products may take any of a wide variety of formsamong which are sheet, strip, bars, rods, tubes, structural andornamental members for inside and outside use such as for automobiles,buildings, stores, restaurants, or the like, ornamental edgings, wallpanels, blocks, frames, furnishings, grills, objects of art andespecially formed, extruded, rolled, or spun articles of manufacture,and that in view of the highly attractive durable finishes achieved, theproducts are most desirable and appealing. Further, machining marks areremoved and the products are made relatively scratch-proof and corrosionresistant by the process. Also it will be noted that our method ishighly commercially feasible and practiced and advances the general artto the end of yielding articles and products having extremely worthwhileornamental and decorative values and widespread utility.

As many possible embodiments may be made of our invention and as manychanges or alterations may be made in the embodiment hereinbefore setforth, it is to be distinctly understood that all matter describedherein is to be interpreted as illustrative and not as a limitation.

We claim:

1. In a method of ornamenting and decorating aluminum base metal fromthe class consisting of aluminum and aluminum base alloys, theimprovement comprising providing said metal in a dead-annealed conditionwith its grains minute in size, cold-deforming said metal equivalent toa reduction of approximately 1% to in thickness thereof, heating thecold-deformed metal for recrystallization to a temperature of about 600F. to 1150 F. for approximately ten minutes to three hours to developlarge crystals in the metal body, said crystals having faces ofmacroscopic size which are visible on the metal surface after etching,etching the surface of said metal in an etching solution to clearlyexpose said crystal faces and their boundaries at said metal surface,making the metal the anode of an electrolytic anodizing bath and forminga corrosion-resistant transparent film of aluminum oxide integral withthe metal on said crystal faces and sealing said film to render itnon-porous, whereby upon viewing said crystal faces through said film,different shadings are seen which differ from crystal face to crystalface.

2. In a method of ornamenting and decorating aluminum base metal fromthe class consisting of aluminum and aluminum base alloys, theimprovement comprising providing said metal in a dead-annealed conditionwith its grains minute in size, cold-deforming said metal equivalent toa reduction of approximately 1% to 15% in thickness thereof, heating thecold-deformed metal for recrystallization to a temperature of about 600F. to 1150" F. for approximately ten minutes to three hours to developlarge crystals in the metal body, said crystals having faces ofmacroscopic size which are visible on the metal surface after etching,etching the surface of said metal in an etching solution to clearlyexpose said crystal faces and their boundaries at said metal surface,making the metal the anode of an electrolytic anodizing bath and forminga corrosion-resistant film of aluminum oxide integral with the metal onsaid crystal faces, dyeing said oxide film overlying said crystal facesto impart a visual characteristic to said crystal faces viewed throughsaid oxide film, and sealing said film to render it nonporous, wherebyupon viewing said crystal faces through said film, ornamental anddecorative shades and hues of color differing from crystal face tocrystal face are observed.

3. A method as claimed in claim 1 wherein said metal is cold-worked byrolling after said recrystallization step and before said anodizingstep, whereby said crystals are appreciably elongated in the directionof said rolling as viewed in plan on said visible surface and havinggenerally the same direction of attenuation.

4. A method as claimed in claim 1 wherein said aluminum metal is clad toa backing sheet of metal which is stronger than said aluminum metal.

5. A method as claimed in claim 1 wherein said metal is an alloy ofaluminum which is solution heat-treated after said recrystallizationstep and before said anodizing step to increase the hardness withoutchanging the size of said large crystals.

6. A method as claimed in claim 1 wherein said metal is work-hardenedafter said recrystallization step and before said anodizing step toincrease the hardness of said large crystals.

7. A method as claimed in claim 1 wherein said coldworked metal isheated to a temperature of about 600 F. to about 1150 F. at a heat-uprate of not more than 1000 F. per hour.

8. A method as claimed in claim 1 wherein said metal is formed into afinished article of manufacture after said recrystallization step andbefore etching.

9. An ornamental decorative aluminum metal product having acorrosion-resistant non-porous transparent surface of aluminum oxide,comprising crystals in the body of said metal disposed in physicalrelief and having etched crystal faces of macroscopic sizes on thevisible surface of the metal made by the process of claim 1.

10. An ornamental decorative aluminum metal product having acorrosion-resistant non-porous transparent surface of aluminum oxide,comprising crystals in the body of said metals disposed in physicalrelief and having etched crystal faces of macroscopic sizes on thevisible surface of the metal made by the process of claim 2.

11. An ornamental decorative aluminum metal product having acorrosion-resistant non-porous transparent surface of aluminum oxide,comprising crystals in the body of said metal disposed in physicalrelief and having etched crystal faces of macroscopic sizes on thevisible surface of the metal made by the process of claim 3.

12. An ornamental decorative aluminum metal product having acorrosion-resistant non-porous transparent surface of aluminum oxide,comprising crystals in the body of said metal disposed in physicalrelief and having etched crystal faces of macroscopic sizes on thevisible surface of the metal made by the process of claim 4.

References Cited in the file of this patent UNITED STATES PATENTS2,050,069 Smith Aug. 4, 1936 2,165,027 Bitter July 4, 1939 2,186,721Guild Jan. 9, 1940 2,262,696 Nook et al. Nov. 11, 1941 2,363,339 Kraftet al. NOV. 21, 1944 2,538,317 Mason et al Jan. 16, 1951 2,647,865 FreudAug. 4, 1953 2,683,113 Prance et al. July 6, 1954 2,703,781 Hesch Mar.8, 1955 2,769,265 Page Nov. 6, 1956 2,780,591 Frey Feb. 5, 1957 FOREIGNPATENTS 763,336 Great Britain Dec. 12, 1956 OTHER REFERENCES The Natureof Metals, Bruce A. Rogers (1951), American Society for Metals,Cleveland, Ohio, and The Iowa State College Press, Ames, Iowa, pages-185.

1. IN A METHOD OF ORNAMENTING AND DECORATING ALUMINUM BASE METAL FROMTHE CLASS CONSISTING OF ALUMINUM AND ALUMINUM BASE ALLOYS, THEIMPROVEMENT COMPRISING PROVIDING SAID METAL IN A DEAD-ANNEALED CONDITIONWITH ITS GRAINS MINUTE IN SIZE, COLD-DEFORMING SAID METAL EQUIVALENT TOA REDUCTION OF APPROXIMATELY 1% TO 15% IN THICKNESS THEREOF, HEATING THECOLD-DEFORMED METAL FOR RECRYSTALLIZATION TO A TEMPERATURE OF ABOUT600*F. TO 1150*F. FOR APPROXIMATELY TEN MINUTES TO THREE HOURS TODEVELOP LARGE CRYSTALS IN THE METAL BODY, SAID CRYSTALS HAVING FACES OFMACROSCOPIC SIZE WHICH ARE VISIBLE ON THE METAL SURFACE AFTER ETCHING,ETCHING THE SURFACE OF SAID METAL IN AN ETCHING SOLUTION TO CLEARLYEXPOSE SAID CRYSTAL FACES AND THEIR BOUNDARIES AT SAID METAL SURFACE,MAKING THE METAL THE ANODE OF AN ELECTROLYTIC ANODIZING BATH AND FORMINGA CORROSION-RESISTANT TRANSPARENT FILM OF ALUMINUM OXIDE INTEGRAL WITHTHE METAL ON SAID CRYSTAL FACES AND SEALING SAID FILM TO RENDER ITNON-POROUS, WHEREBY UPON VIEWING SAID CRYSTAL FACES THROUGH SAID FILM,DIFFERENT SHADINGS ARE SEEM WHICH DIFFER FROM CRYSTAL FACE TO CRYSTALFACE.